Wanting "High End Power" on RM 250

[Hooner33]

Hey, Im looking for a little help and Im open to any suggestion on how to get more top end power out of my 98 RM 250. I have heard that this year RM 250 didn't have much to start with in the begining.
Heres the bike:
98 RM 250 with,
1. 13 tooth front, 52 tooth rear sprocket
2. 14oz flywheel weight
3. Bills Pipe
4. Stock silencer
5. Original top end and bottom end. (BTW only 14 hours on the bike)
6. Tech Care suspension
and a bunch of kick a** flashy racing graphics, renthal bars, skid plate, excel wheels, bark busters, and one 21 yr old (5'7 and 175 lbs kid who doesn't like to go slow :laugh: )

I have GREAT low end power, but i have to fly through the gear box quickly because the top end power is a little, how you say, " Sh*ty"! The top end power doesn't bog down or need to be rejetted. I have done it and found a sweet spot. I simply want to go faster through the high end power.

 

[76GMC1500]

FMF Rev pipe, reeds, cylinder porting...

 

[adam728]

Eric Gorr's "Motocross & Off-Road Performance Handbook" recommends frequent powervalve maintanance, filing the powervalve so that it sits flush with the top of the exhaust port when open, and cylinder porting (widening and raising the exhaust port).

Different reeds, retarded timing, and a lighter flywheel could all help as well.

 

[CRazy250]

changing the pipe will change bottom end power, but go with the fmf rev if your willing to sacrifice bottom end for top end power

 

[mongial]

I have an 02 RM 250 that has a ton of bottom and Mid. I ride wide open desert or tight nasty cross country desert. When I am in the wide open terrain I run a 14 countershaft with an FMF SST pipe (amazing difference) and for the tight slow stuff I run a Bill's Pipe with 13 on the front. If your lucky you can purchase a Fatty, SST, or Rev on that auction site used for around $50.

 

[flyinzuki]

You could add 1 or 2 extra base gaskets, or call Cometic and they will make the thickness you want.

Change gearing... I run a 49 in the woods.
13 - 52 is for pulling trailers :whoa:

 

[cr85rb_rider]

Ok what exacltly will adding a base gasket do to the performance?

 

[kx125412]

Did anyone read he had a flywheel weight? Get rid of that if you want high end power. The weights just getting you better traction down low and hurting the top somewhat. The weights good for tight trails and technical stuff. Not if you just wanna rev it nice and high.

 

[flyinzuki]

It will raise the ports, which will let the motor rev out a little more.
However it will lower compression, and increase squish clearance, which will weaken the low- mid.
That's why specific porting and matching head mods work.

Regarding the flywheel weight.
His complaint is that he has to go through the gears to fast allready.

 

[4thGearAndPinned]

fiddle with gearing, or buy a different bike.

 

[2-Strokes 4-ever]

Porting will find you huge gains. A pipe will help, but it will not be at all the gain that cylinder work will do. Pipe = quick "sort of" fix. Motor design = a good foundation to work with.

 

[76GMC1500]

A friend of mine used to have a 1997 YZ 250 that made horsepower to compete with a 500. This bike had the most ridiculous top end of any bike I have ridden to date. The bike had a spacer installed at the bottom of the cylinder, probaby 5mm thick and had a special piston/headwork and a longer connecting rod to keep the compression ratio reasonable. It also had an FMF Rev pipe. Does anybody make a similar setup today?

 

[Hooner33]

Well, i would like to thank you for all of your ideas and tips, I would like to keep the flywheel weight do to the fact that I only rid ethe woods and it works well and is a little more controlable throtle response. I'll change the silencer and look into the porting mods.